David Cameron's plan to legalize gay marriage in Britain will cost the party votes, a new poll has found.

The British prime minister backs a plan to move gay and lesbian couples from civil partnerships to full marriage by sometime next year. Under the plan, gay couples would be allowed to marry in a church.

According to the ComRes survey of 544 UK Christians, 83 percent of churchgoers oppose the idea, while 57 percent said the idea made them less likely to vote for the Conservative Party, of which Cameron is the head.

A near universal majority (90%) of those surveyed said they feared allowing gay couples to marry would lead to schools being required to teach that a gay marriage is equal to a heterosexual marriage and that clergy would be forced to officiate over the weddings of gay couples against their consciences. Eighty-five percent said marriage equality would undermine the institution of marriage.

“The Government is consulting on introducing civil marriage for same-sex couples,” the Conservative Party said in a statement. “There is no question of churches or any other religious institution being forced to host ceremonies for same-sex marriage or for civil partnerships.”

“We believe society is stronger when we make vows to each other and support each other. That is why we support gay marriage.”

The online survey was conducted between October 25 – 31.

(Related: David Cameron makes conservative case for gay marriage.)